X-Ray Tetra (Pristella maxillaris)

Distribution: Amazon River basin throughout northern South America (esp. the Amazon, Orinoco and Guianan coastal drainages)
Length: 1.75"
Water Temperature: 73 to 82 degrees Fahrenheit (23-28 degrees Celsius)
Diet: Aquatic insect larvae in the wild; most commercially-prepared foods will work extremely well for these fish, especially when supplemented with some of the commonly-available small live foods.
Water Chemistry: Largely unimportant, even for spawning (M. P. Smith)
pH: 6.0-8.0 is a good target
Lifespan: 5 years

Species Description I like Mark Phillip Smith's statement that this "...is a desirable Characin, with most of its chromatic appeal concentrated in its fins." That is quite true, as the body of this fish, which looks like a horizontally stretched Black Widow Tetra in profile, is a translucent silver. (That is still pretty striking, but the fins draw attention away from it.)

The caudal fin is silver near the peduncle, but quickly becomes a reddish-orange coloration that can only be described as striking. The dorsal is clear near its peduncle and throughout its trailing third but its leading two thirds have white stripes sandwiching a black dot. The fins below the lateral line are generally clear closest to the body, then yellow, then black and then white. For the anal fin, however, this coloration only appears in the first rays, which have much more length than their trailing counterparts. The latter are merely clear.

A morph called the Gold X-Ray is actually an albino variant of the wild type and has become increasingly available in recent years, though it is not likely to replace the wild type in the aquarium hobby (as albino morphs of other fishes have done).

Species Behaviour Though among the hardiest of tetras, X-Rays have a well-deserved reputation for shyness, especially amongst larger or more boisterous fishes. They will shoal loosely even when feeling at their best, but a tightly-shoaled group of X-Rays is extremely nervous; the stimulus for this nervousness should be corrected at once, if at all possible.

Natural Conditions Thrives in many conditions from small creeks to slow-flowing sections of larger rivers. FishBase puts them in densely-vegetated swamps and calm coastal waters; perhaps placing a good deal of plants in their aquaria isn't a bad idea. (The vegetated swamp part is covered in M. P. Smith's breeding account, wherein he suggests the usage of java moss or spawning mops at the bottom of the spawning aquaria.)

Sexing Males have a tendency toward being slimmer than their female counterparts.

Breeding Smith calls them "Great beginner Characins to start out with" in his 'Reproduction' section on the Pristella Tetra. They'll generally spawn amongst java moss on the bottom of the aquarium or spawning mops in the same position. Once spawning activity has ceased, remove the parents as they will eat their eggs.

The fry are very small and Smith recommends green water and infusorians for them as first foods, while other sources recommend baby brine shrimp.

Feeding Aquatic insect larvae in the wild; most commercially-prepared foods will work extremely well for these fish, especially when supplemented with some of the commonly-available small live foods.